Light source and light-sensitive coating for phonocinematography



June 29 1926. 1,590,185

J. ENGL ET AL LIGHT SOURCE AND LIGHT SENSITIVE COATING FOR PHONOCINEMATOGRAPHY Filed April 4, 1921 INTENSITY OF LIGHT M I f/J/70AS PASSING THROUGH 1 $epZ/VZ Jayeflwu sow T THICKNESS 0F EMULslou COATING QTYUAWEYS Patented June 29, 1926.

UNITED, STATES PATENT OFFICE.

JOSE! ENGL, OF GRUNEWALD, HANS VOGT, OF BERLIN-SCHONEBERG, AND JOSEPH IASSOLLE, OE GRUNEWALD, GERMANY, ASSIGNORS TO TRI-ERGON LIMITED, 01

ZURICH, SWITZERLAND.

LIGHT SOURCE AND LIGHT-SENSITIVE COATING FOR DHONOCINEMATOGBAPHY.

Application filed April 4, 1921, Serial Ito. 458,684, and in Germany December 22, 1819.

It is known to record by photography the intensities of sound from any source as variations of degree of blackening of, for instance, the silver bromide coating of a mov- 5 ing film. For the reproduction of such photophonograms an optico-electrical method is employed. A small portion of the film is illuminated by an intense source of light of suitable form. The light allowed to pass I" through the film in accordance with the photog'raphical blackening is concentrated onto an electrical device, (photoelectric cell), in which it sets up electric currents Whose strength is dependent upon the energy of radiation, received by the-cell, that is to say, according to the degree of absorption of light by the silver bromide coating on the film. When the film moves past the cell an electric acoustically-modulated current is generated, in a circuit including the cell,

which current can again be converted into sound waves. 4

According to theinvention sources of light are used, whose light emission is so adapted to the absorption properties of the coating constituting the photophonogram that the fluctuations in the light radiations which impinge upon the photoelectrical device, and consequently the variations in amplitudes of the wave current produced in the circuit of the photoelectric cell, are as great as possible.

In accordance with the invention, also, the photoelectric cell is chosen so as to have maximum or desired sensitiveness to the wave-length of light principally emitted by the light source. The invention is predicated upon the use of a selective light source. that is, one which chiefly emits light. of a certain range of wave-lenlgl'ths, or rays ofi light at a desired part of t e spectrum, and

using therewith a film the coating of which I is particularly absorptive ofi such rays; and also using with such source a light-responsive cell the cathode or light-sensitive element of which is particularly sensitive to such rays. This is based upon the observation that difierent forms of emulsion are absorptive of, or, conversely, are 5 ermeable by,difi'erent ranges of light waveengths, to different extents; and also that the light-sensitive materials possible for use in the photo-cell are sensitive to different light wave-lengths'to difierent extents.

produced y the said fluctuating current,

than if the light source and emulsion coating were not thus related to each other. The effect of using, with said selective light source, a photo-cell of greatest sensitiveness for the light emitted by that cell, is to give greater amplitude to the current produced by the cell, and therefore greater intensity of sound finally produced, than if the source and cell were not thus related to each other.

In the accompanying drawings, Figure 1 1s a diagram wherein the manner of the absorption of two different radiations for vary ingthicknesses of the film emulsion coating is represented by curved lines, the horizontal co-ordinate of the diagram representing the thickness of the light-absorbing layer on the film, and the vertical co-ordinate representing the intensity of light allowed to pass through the film; and

Figs. 2 and 3 are diagrammatical views, each showing the apparatus in connection with which the present invention may be employed, Fig. 3 being takenat right angles to ig. 2.

It will be understood that the photographic sound record formed on the emulsion coating of the film varies in intensity, that is to say, by variation in density or thickness of the emulsion coating corresponding to variations of intensity of the original sound fvvlhich'is photographically recorded on the The manner in which emulsion coatings vary in light absorptive properties when subjected to radiations of different characters is illustrated in the diagram Figure 1. If the thickness of the emulsion coating on the film increases, for example, from value one to value two in the diagram, the amount a according to curve a, from S to S... By

' bounda the selection of a source of light whose radiation, corresponding to curve a, has a high co-eificient of absorption in the emulsion coating of the photo honogram carrier, it is thus possible to ma e the varyingamplitudes of the wave current to be converted into acoustic waves, as great as possible. That is to say, the increased variations of amplitude of the fluctuating current produced by the photoelectric cell are thus increased by the conjoint use of a source ofi 1i ht, the ra s chiefly emitted by which are of a particu ar character with an' emulsion coating on the film which is particularly absorptive of such rays.

In order that the effect of the radiation through the emulsion coating, u n the photoelectric cell or other light sensitive device, shall be as large as possible, the photoelectric device is chosen with absorption properties which are dependent upon the nature of the li ht source, since the sensitivity to light 0 such devices, throughout a considerable range of wave-lengths, can be adjusted to certain wave-lengths. That is to say, a current of maximum strength will be provided by the photoelectric device or light responsive device used, the light sensitive element of which has maximum sensitiveness for the rays chiefly emitted by the particular source of light used.v

The invention can be practiced in various ways. For exam 1e, for the source of light, a mercury vapor am may be used in which the vapor is rendere luminous by the passage of an electric current therethrough. This lamp may be the intensely luminous quartz lamp, known in science for other purposes, in which the major portion of the radiation intensity is located atv the short wave of the visible spectrum and within the u tra violet range. With such a light source, a photoelectric cell should be used, the maximum sensitivity of which lies within this ortion of the spectrum, for instance an alka photoelectric cell having a cathode of metallic sodium.

If an emulsion coating of silver of varying permeability be used as represented for instance by a film havin a photographic imprint which has been eveloped, the absorptivit of the thin silver coating is minimum for light rays of wave-len hs correszlonding to' the violet and ultra vio et end of e spectrum. Because silver coatings are particularly permeable for li ht of such wavelengths, they are repl in accordance with this invention by emulsion coatings of mercury or copper, for example when the light source is a mercury va r lamp. Therefore, in this example the lig t source emits largely the ultra violet rays, which pass most easily through the quartz glass of the lamp; the film co'ating has maximum abso tion properties for'such rays and the oath e of the photo cell has maximum sensitivity for such rays.

In the selection of the source .of light it must further be taken into consideration that it is desirable to filter out all the radiation energy otherthan the rays for which the particular light source is selected. That is to say, in the above example the infra red and the rest of the visible radiations may be screened out by the provision of suitable light filters located between the source of light and the film, since this portion of the light emitted by the source is unnecessary and may render the technical solution of the problem of reproducing sound vibrations impossible. For this reason and also on account of the well known spectral selectivity of the photoelectric device, it is generally of advanta e to use sources of light, the radiation 0 which has a selective character. Radiating bodies which possess a continuous emission spectrum, such as heated solid bodies (metallic wires, Nernst lowers, incandescent carbon electrodes of t e light are, etc.) are therefore less suitable. Light sources with selective radiation are, for example, metallic vapors which have been rendered luminous by an electric discharge of" currents of high intensity. Selective light sources which may thus be used are mercury, cadmium and zinc lamps, which are well known in the technical arts for other uses. A cadmium vapor lamp, for instance, might be used with a photoelectric cell having a cathode of rubidium as the photoelectric element of maximum sensitivity for use with this particular li ht source. The cadmium lamp chiefly produces red -ra s and the rubidium cell may be used wit it since it is most sensitive to the red rays. A film coating of maximum absor tivity for these red rays should, of course used.

We claim:

1. In sound reproducing apparatus, the

combination of a source of light, a; lightsensitive cell, and a transparent film having a sensitive emulsion coating thereon, movable between the light-source and cell said character as to be more absorptive of such rays than of light rays at other parts of the spectrum.

2. In sound reproducing ap aratus, the

.combination of a source of hg t, a lightsensitive cell, and a transparent film having .a sensitive emulsion coating thereon, movablezbetween the light-source and cell,-

said coating havin a photogra hic sound record of varying h ght-permeability formed 1 combination of a sensitive cell, and a trans thereon; said source being a luminous metallic vapor having a spectral selectivity such that it chiefly emits light rays belonging to only one part of the spectrum, said cell having a light sensitive element which is most sensitive to such rays, and the ooating on the film being of such character as to be more absor tive of such rays than of light rays at other parts of the spectrum.

3. In sound reproducing apparatus, the

source of light, a lightparent film having a sensitive emulsion coating thereon, movable between the light-source and cell, said coating having a photographic sound record of varying lightrpermeability formed thereon; said source being a luminous metallic vapor lamp having a spectral selectivity suoh'that it chiefly emits light rays at the short wave end of the visible spectrum and in the ultra violet r 'on, said cell having an alkali cathode which is most sensitive to said rays, and the coating on the film being a layer of mercury, adapted to be more absorpltive of such rays than of light rays at ot er parts of the spectrum.

4. In sound reproducing apparatus, the combination of a source of light, a lightsensitive cell, and a transparent film having a sensitiveemulsion coating thereon, movr able between the lightrsource and cell, said coating having a photographic sound record of varying light-permeabilityformed thereon; said source being a mercury vapor lamp emitting rays of greatest intensity at the short wave end of the visible spectrum and. in the ultra-violet region, said cell hav. ing a sodium cathode, and the coating on the film comprising a layer of mercury.

5. In sound reproducing apparatus, the combination of a light source of spectral selectivity such that it chiefly emits light rays belon ing to only one part of the spectrum, a pfioto-celh'and a transparent film movable between the light-source and cell and light filtering means between said source and film for screening out rays of the other Wave-lengths than those chiefly emitted by said source, said film having a sensitive emulsion coating thereon having a photographic sound record in which vary- 1ng intensities of sound are re resented by lines or portions of correspondingly varying density or thickness of emulsion, said emulsion coating being of such character as to be more absorptive of rays of the wave-lengths chiefly emitted by said source than of light rays at other parts of the spectrum.

6. A process of reproducin sound, com,- prising, selecting a source of ight of spectral selectivity such that it emits light rays of greatest intensity at a desired part of the spectrum, selecting a film for a photographic sound record having an emulsion coating 0" such a character as to be more absorptive o; rays of the wavelengths chiefly emitted by said source than of li ht-rays at other parts of the spectrum, producing on such film a photographic sound record in which varying intensities of sound are re resented by lines or portions of correspondingly varying density or thickness of emulsion, and selecting a photoelectric cell having a light sensitive element which is most sensitive to such rays, progressing said film between said source and said cell so that li ht from said source will pass through sai film to greateror less degree and fall upon the light sensitive element of said cell, said cell being connected in a circuit in which a sound modulated current will flow, and causing such current to reproduce the sound.

In testimony whereof we afiix our signas tures.

DR. JOSEF ENGL. HANS VOGT. JOSEPH MASSOLLE. 

